Blood Components, Types, Circulation

Alkanes (CnH2n+2)

Alkanes: Hydrocarbons with only single carbon-carbon bonds.

• General Formula: C$_{n}$H$_{2n+2}$
• Carbon atoms exhibit sp3 hybridization.
• Form a homologous series:
  • Differ by a CH$_{2}$ group.
  • Same general formula and functional group.
  • Similar chemical properties.
  • Gradual change in physical properties (e.g., molar mass, melting/boiling points, density).

Key Properties of Alkanes

• First 10 straight-chained alkanes (e.g., methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane).
• Derived from crude oil via fractional distillation and cracking.
  • Cracking converts longer chains to shorter, more valuable ones.
    • Catalytic cracking: ~500°C with catalysts.
    • Thermal cracking: ~800°C without catalysts.
• Different formula representations: Molecular, condensed, structural.

Nomenclature (Naming) of Alkanes

IUPAC system:Standardized naming for global scientific communication.

• Unbranched alkanes: Latin prefix for carbon count + -ane suffix.
  • Example: Meth-ane, eth-ane.
• Substituent Alkyl Groups:
  • Formed by removing one H from an alkane.
  • General formula: C$_{n}$H$_{2n+1}$.
  • Suffix changes from -ane to -yl.
    • Example: Methane (CH$_{4}$) becomes meth-yl (-CH$_{3}$).
    • Represented by "R".

Rules for Naming Branched Chain Alkanes

1. Longest continuous carbon skeleton is the parent chain.
2. Groups/atoms outside the skeleton are substituents.
3. Number carbon atoms to give substituents the lowest possible numbers.
4. Substituents arelisted in alphabetical order.
5. Number and name are separated by a hyphen (-).
6. If two different substituents have equal positions from opposite sides, prioritize by alphabetical order.
7. Multiple identical substituents use Latinprefixes (di-, tri-, tetra-, etc.) and comma-separated numbers.
8. Ignore di-, tri- for alphabetical ordering; iso-, neo- are considered.

Common Names of Alkanes

• n-: No branching (normal).
• iso-: One methyl group on the second carbon. (e.g., isobutane).
• neo-: Two methyl groups on the second carbon. (e.g., neopentane).

Isomerism in Alkanes

Isomers: Compounds with the same chemical formula but different arrangements.

• Chain isomerism: Straight vs. branched chains.
• Alkanes with >3 carbons show chain isomerism (e.g., butane has 2 isomers).

Physical Properties of Alkanes

• Colourless and odourless.
• Gases: 1-4 carbon atoms.
• Liquids: 5-17 carbon atoms.
• Solids: 18+ carbon atoms.
• Melting/boiling points increase with chain length.
• Nonpolar molecules:Insoluble in water, soluble in organic solvents.
• Lower density than water, so they float.

Chemical Properties of Alkanes

• Undergo combustion with oxygen: Alkane + O$_{2}$ → CO$_{2}$ + H$_{2}$O + energy.
  • Complete combustion: Excess O$_{2}$ → CO$_{2}$ + H$_{2}$O.
  • Incomplete combustion: Limited O$_{2}$ → CO +H$_{2}$O or C (soot) + H$_{2}$O.
• Do not undergo addition reactions (due to single bonds).
• Undergo substitution reactions with halogens under UV light (free radical substitution).

Uses of Alkanes

• Natural gas: Primarily 1-4 carbon alkanes.
• Gasoline and kerosene: Liquid alkanes.
• Paraffin wax (solid alkanes): Candles, anti-corrosive agents, lubricating oil.
• Higher alkanes are cracked for various uses.

Synthesis of Alkanes

1. Hydrogenation of Alkenes: Add H$_{2}$ acrossdouble bond using Pd, Pt, or Ni catalyst.
2. Wurtz Synthesis: Couple haloalkanes using sodium metal in dry ether.
3. Grignard Synthesis: React Grignard reagent (alkyl halide + Mg) with water.

Methane (CH4)

• Physical properties: Colourless, odourless, non-poisonous gas. Nonpolar. Insoluble in water, soluble in ether/alcohol. Very low melting/boiling point.
• Chemical properties:Main component of natural gas. Powerful greenhouse gas (holds 20x more heat than CO$_{2}$). Emitted from anaerobic environments.
• Uses: Fuel (automobiles, ovens, water heaters), electricity generation, antifreeze, fertilizers, sanitizing products.
• Natural Gas Leakage: Natural gas (mainly methane) is odourless; mercaptan is added for detection (rotten egg smell). Leaks reduce available oxygen, causing symptoms like headache, dizziness, nausea.

Alkynes (CnH2n-2)

Alkynes: Unsaturated hydrocarbons with a carbon-carbon triple bond.

• General Formula: C$_{n}$H$_{2n-2}$.
• Carbon atoms in triple bond exhibit sp hybridization.
• Have two fewer hydrogen atoms than corresponding alkenes.

Nomenclature (Naming) of Alkynes

• Similar to alkanes/alkenes: -ane suffix replaced by -yne.
  • Example: Eth-yne, prop-yne.
• Parent chain: Longest carbon chain containing the triple bond.
• Multiple triple bonds: Specify positions and use suffixes like diyne, triyne.
• Priority:If double and triple bonds are equidistant, the double bond gets the smallest number.

Isomerism in Alkynes

• No geometric isomerism (due to linear shape).
• Have structural isomers (chain, position, functional).
• First two members (ethyne, propyne) have only one structure.

Structural Isomerism in Alkynes

• Chain Isomerism: Straight vs. branched chains (e.g., 1-pentyne and 2-methyl-1-butyne).
• Position Isomerism: Different positions of the triple bond (e.g., 1-pentyne and 2-pentyne).
• Functional Isomerism: Alkynes and alkadienes with the same number of carbonatoms.

Physical Properties of Alkynes

• Homologous series.
• Insoluble in polar solvents (water), soluble in organic solvents.
• Smaller alkynes are gases with low melting/boiling points.
• Slightly higher boiling points than alkanes and alkenes.

Reactions of Alkynes

1. Combustion: Produce CO$_{2}$ and H$_{2}$O, releasing heat.
   • Acetylene (ethyne): Used in metal cutting (acetylene torch) due to high heat release.
2. Hydrogenation: Convert to alkenes/alkanes in presence of catalysts.
   • To alkanes: Add twoH$_{2}$ molecules with Pt catalyst.
   • To alkenes: Add one H$_{2}$ molecule with Lindlar's catalyst.
3. Addition of Hydrogen Halides and Halogens: Forms halogenoalkenes andhalogenoalkanes (e.g., addition of HCl to acetylene gives chloroethene).
4. Addition of Water: In presence of acid, produces an enol (alkene with hydroxyl group).
5. Dimerization of Acetylene: Forms vinyl acetylene (used in artificial rubber).
6. Synthesis of Benzene: Acetylene molecules react at ~400°C with catalysts.

Synthesis of Alkynes

1. Synthesis of Acetylene:From limestone, coal, and water in industry (limestone → quicklime (CaO), quicklime + coal → calcium carbide (CaC$_{2}$), CaC$_{2}$ + H$_{2}$O → acetylene).
2. Dehydrohalogenation of Dihalogenoalkanes: Alkynes formed by eliminating two HX molecules using strong bases (e.g., alkoxide bases) at high temperatures.

Importance and Uses of Alkynes

• Acetylene (ethyne): Important industrial starting material.
  • Rocket fuel.
  • Synthesis of organic compounds (ethanoic acid, acrylic acid, ethanol).
  • Organic solvents.
  • Starting material for polymers (e.g., polyethylene plastics, neoprene).
  • Welding andcutting (hottest flame at 3500°C).

Alkenes (CnH2n)

Alkenes: Unsaturated hydrocarbons with a carbon-carbon double bond.

• General Formula: C$_{n}$H$_{2n}$.
• Carbon atoms forming double bond exhibit sp2 hybridization.
• More reactive than alkanes due to double bond.
• Can be converted to alkanesby hydrogenation.
• Multiple double bonds: alkadienes (2 double bonds), alkatrienes (3 double bonds).

Nomenclature (Naming) of Alkenes

• Similar toalkanes: -ane suffix replaced by -ene.
  • Example: Eth-ene, prop-ene.
• Alkenyl group: Formed by removing 1 H atom (e.g., ethenyl, 2-propenyl).

IUPAC Naming of Alkenes

1. Longest carbon chain containing the double bond is the parent chain. Suffix is -ene.
2. Number carbons starting from the end closest to the double bond.
   • If double bond is equidistant, start from end closest to substituent.
3. Specify positions and number of substituents in alphabetical order.
   • Use diene, triene for multiple double bonds.

Isomerism in Alkenes

• Show structural isomerism (chain, position, functional).
• Show stereoisomerism (geometric isomerism / cis-trans isomerism).

Structural Isomerism in Alkenes

• Chain Isomerism: Straight vs. branched chains (e.g., 1-buteneand 2-methylpropene).
• Position Isomerism: Different positions of the double bond (e.g., 1-pentene and 2-pentene).
• Functional Isomerism: Alkenes and cycloalkanes with thesame number of carbon atoms.

Stereoisomerism in Alkenes: Geometric Isomerism (cis-trans isomerism)

Restricted rotation around the double bond leads to cis-trans isomers.

• Cis isomer: Groups on the same side of the double bond.
• Trans isomer: Groups on opposite sides of the double bond.
• No cis-trans isomerism if:
  • 3 identical groups attached to double bond carbons.
  • Same groups attached to one of the double bond carbons.

Physical Properties of Alkenes

• Homologous series.
• Nonpolar, insolublein water, soluble in organic solvents.
• Less dense than water.
• Gases: 4 or fewer carbon atoms.
• Liquids: 5-17 carbon atoms.
• Solids: >17 carbon atoms.
• Lower melting/boiling points than corresponding alkanes.

Reactions of Alkenes

More reactive than alkanes; undergo addition reactions.

1. Hydrogenation: Addition of H$_{2}$ across double bond with Pt, Pd, or Ni catalysts, forming saturated alkane. (Exothermic)
2. Halogenation: Addition of Cl$_{2}$ or Br$_{2}$ across double bond,forming dihalide. (Iodine too slow; Fluorine too vigorous).
3. Addition of Hydrogen Halides (H-X): Produces alkyl halide.
   • For unsymmetrical alkenes, regioselectivity is important (which carbon gets H vs. X).
4. Addition of Water (Hydration): In presence of strong acid catalyst, forms alcohols.
5. Oxidation: Increase C-O bonds, decrease C-H bonds.
   • Syn 1,2-Dihydroxylation: Forms 1,2-diol (hydroxy groups added on same side) using OsO$_{4}$ or KMnO$_{4}$.
   • Ozonolysis: With ozone at -78°C, followed by reduction, oxidizesalkenes into aldehydes or ketones.
6. Polymerization: Addition polymerization of monomers to form polymers (e.g., ethene to polyethene).

Synthesis of Alkenes

1. Dehydrohalogenation of Alkyl Halides: Elimination reaction (1,2-elimination) using strong bases (e.g., NaOH, KOH) with heating.
2. Dehydration of Alcohols: Elimination of water from alcohol by heating withstrong acid (e.g., H$_{2}$SO$_{4}$, H$_{3}$PO$_{4}$) at high temperatures.

Importance and Uses of Alkenes

• Ethylene: Plant hormone for fruit ripening (commercial use for bananas, tomatoes).
• $\beta$-carotene: Vitamin A source, polyalkene with 11 double bonds.
• Starting materials for polymers (e.g., ethylchloride, ethanol, polyethylene).
• Artificial polymers: Polyethylene (PE), polyvinyl chloride(PVC), polystyrene, polytetrafluoroethylene (Teflon) are derived from alkenes or their derivatives.